Thank you very much for your patience! I did find the cause. Pressing “home” returns wrong result for native command getSelection(). Instead of the text node it gets back the li node. This happens for:

You could try submitting a Gecko bug (or see if it has already been reported), since that definitely seems like a bug (home/end selection motion should happen within the current text block—moving to the list node when pressing home in an list item is just weird).